One more word order problem :(
A. They both have to abide by his decision
They have both to abide by his decision
B. How could a fine or other punishment be described if a magistrate is free to decide whether to award it or not?
How could a fine or other punishment be described if a magistrate is free to decide whether or not to award it?
Not a teacher, am a native.
For A, the first choice. No need to split the verbs. Keep them together. "have to abide." This also keep the nouns together. "They both." Or "Both of them," but "they both" is OK.
For B, either is fine. Neither is wrong. I'd probably choose the first, but the second is not wrong or unintelligble.